Microelectromechanical (MEM) systems are getting a significant amount of attention in the field of optical switches. MEM technology generally involves the fabrication of small mechanical devices on a silicon substrate, together with electronic circuitry for actuating motion of the mechanical device. Surface micromachining is one type of fabrication technique for MEM systems. Surface micromachining generally entails depositing alternate layers of structural material and sacrificial material on an appropriate substrate, such as a silicon wafer, which functions as a foundation for the resulting microstructures. Various patterning operations may be executed on one or more of these layers before the next layer is deposited so as to define the desired microstructures. After the microstructures have been defined in this general manner, the various sacrificial layers are removed by exposing the microstructures and the various sacrificial layers to one or more etchants which “releases” the resulting microstructures from the substrate (e.g., to allow relative movement).
A MEM-based optical system may include multiple mirror microstructures formed on a substrate for making optical connections. Each mirror microstructure may be interconnected with at least one lift assembly, one or more actuators, and one or more displacement multipliers. The lift assembly may be used to raise the mirror microstructure above the plane of the substrate and/or tilt the mirror into an appropriate position to provide a desired optical function. The actuators are attached to the substrate so as to be movable relative thereto, and provide the motive force/displacement that is used to raise/tilt these mirrors. Electrostatic actuators are commonly used in these types of systems. These types of actuators produce a short stroke displacement which may be insufficient to raise/tilt the mirror to a desired level in at least certain instances. Therefore, the noted displacement multiplier(s) is typically disposed between the actuator and its associated lift assembly to increase the displacement provided by the actuator to the lift assembly, and to thereby allow the mirror microstructure to be raised/tilted to a desired degree. One example of a displacement multiplier is disclosed in U.S. Pat. No. 6,175,170.
Displacement multipliers may be designed to produce a relatively large output based upon a relatively small input. However, displacement multipliers can become rather intricate, which increases development costs. Moreover, displacement multipliers often require a significant amount of space on a die. Since there is only a fixed amount of space within a die for fabrication of the microelectromechanical system, the use of one or more displacement multipliers may reduce the mirror density within the die. Although this may be acceptable for certain applications, a higher mirror density may be desirable for other applications. Therefore, it would be desirable to achieve displacement multiplication for a microelectromechanical system in a manner that allows for increased mirror density.
A tether or the like may be disposed within the interconnection between a mirror elevator and the actuator(s). For instance, an actuator or a plurality of actuators may be interconnected with an input to a displacement multiplier, and the tether may interconnect the output of the displacement multiplier with the mirror elevator. This mirror elevator may have a free end that moves away from and toward the substrate, depending upon the direction of the movement of the actuator(s). This then raises and/or tilts a mirror that may be interconnected with the elevator.
One previously contemplated configuration for the above-noted tether was to form the same from a single layer of a structural material in a surface micromachined optical system. This resulted in the tether being flexible.